Conventional lamp curing technology based on gas discharge lamps, such as mercury arc lamps, emit broad spectrum UV radiation generally from 300 nm (mid-UV range) to approximately 570 nm, with several characteristic emission lines making up the spectral content. Gas discharge lamps require high voltages to operate, have short lifetimes of approximately 15,000 hours, and require active cooling to maintain stable operation, making the costs of operation high.
With the advent of gallium nitride (GaN) based LEDs, the ability to create solid-state, semiconductor semiconductor light sources with high enough UV energies, (shorter wavelengths), has given rise to LED-based curing lamps. GaN LED technology enables curing lamps that are more compact with lower input power requirements, lower operating costs, and longer lifetimes. While LED-based curing lamps offer clear advantages over gas discharge lamps, they are typically limited to a single wavelength (e.g. 395 nm or 365 nm for UVA curing applications). As such, most UV-cured materials may require adjustments in formulation to cure efficiently at 395 nm or other singular wavelengths. However, there remain applications and systems that require a broader spectral content for efficient and complete curing, such as the emission spectra afforded through the use of conventional mercury arc lamps.
Kurtin et al. disclose a lighting apparatus including an LED emitting blue or UV light and a plurality of quantum dots. The quantum dots may be applied proximal to the LED and provide down-conversion or upshifting of blue or UV light emitted from the LED to emit red, green, yellow, orange, blue, indigo, violet or other visible light having a wavelength from 380-780 nm. Kurtin further discloses that the absorption and emission spectrum of each quantum dot are essentially non-overlapping.
The inventors herein have recognized potential issues with the above approach. Namely, Kurtin is directed to providing a lighting apparatus for emitting visible light. In particular, Kurtin is directed to absorbing and down converting blue and UV light to visible light via quantum dots, and emitting the visible light therefrom. As such, Kurtin's lighting apparatus does not address the problem of providing broad emission spectra for UV curing such as that of conventional mercury arc lamps. Furthermore, Kurtin's lighting apparatus does not emit UV radiation below 380 nm. Accordingly, Kurtin's lighting apparatus is not suited for applications requiring a broad UV spectral content for efficient curing.
One approach that addresses the aforementioned issues includes a curing device, comprising a first array of LED's, each LED of the first array emitting radiation substantially centered at a first excitation wavelength onto a quantum dot layer, the quantum dot layer positioned above the first array of LED's and configured to partially absorb the first excitation wavelength radiation and down convert the absorbed first excitation wavelength radiation, and partially transmit the emitted first excitation wavelength radiation, wherein the down converted and the partially transmitted first excitation wavelength radiation are directed onto a radiation-curable workpiece.
In another embodiment, a method of curing a workpiece, comprises emitting radiation substantially centered at a first excitation wavelength from an array of LED's onto a quantum dot layer, only partially transmitting the first excitation wavelength radiation through the quantum dot layer onto a radiation-curable workpiece, only partially absorbing the emitted first excitation wavelength radiation at the quantum dot layer, and responsive to absorbing the excitation wavelength radiation, down converting the absorbed first excitation wavelength radiation at the quantum dot layer and emitting the down converted radiation onto the radiation-curable workpiece.
In a further embodiment a method, comprises emitting UV radiation onto a quantum dot layer, only partially absorbing and down converting the UV radiation substantially centered at 365 nm at the quantum dot layer, and only partially transmitting the UV radiation substantially centered at 365 nm through the quantum dot layer.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.